Defrost control responsive to air pressure differential

ABSTRACT

IN THE PREFERRED FORM, A TUBE THROUGH WHICH AIR CIRCULATES EXTENDS INTO HEAT TRANSFER RELATION WITH THE PORTION OF THE EVAPORATOR AND THE SUCTION LINE. THE ACCUMULATION OF FROST WITHIN THE TUBE IS PROPORTIONAL TO THE AMOUNT OF FROST WHICH ACCUMULATES ON THE EVAPORATOR. A THERMOSTAT BULB IS MOUNTED IN HEAT TRANSFER RELATION WITH THE OUTLET PORTION OF THE TUBE AND IS NORMALLY COOLED BY THE AIR FLOW THROUGH THE TUBE. IT OPERATES A DOUBLE THROW SNAP SWITCH FROM THE NORMAL REFRIGERATING POSITION TO DEFROST POSITION WHEN THE TUBE REACHES A PREDETERMINED HIGHER TEMPERATURE TO INITIATE A DEFROSTING OPERATION. A SECOND CONTROL RESPONSIVE TO THE DIFFERENCE IN PRESSURE IN THE INLET AND OUTLET PORTIONS OF THE AIR TUBE OPERATES A DOUBLE THROW SWITCH WHICH MAY BE CONNECTED IN PARALLEL WITH THE PREVIOUSLY MENTIONED SWITCH TO PROVIDE A SECOND DEFROST AIR CONTROL WHICH OPERATES WHEN THE PRESSURE DIFFERENTIAL INCREASES TO A PREDETERMINED AMOUNT TO OPERATE THE DOUBLE THROW SWITCH FROM NORMAL REFRIGERATION POSITION TO THE DEFROST POSITION. IN A SECOND FORM OF THE INVENTION AIR IS DRAWN THROUGH A TUBE LOCATED IN HEAT TRANSFER WITH THE EVAPORATOR BY THE VACUUM OF THE INTAKE MANIFOLD OF A GASOLINE ENGINE. WHEN FROST RESTRICTS THE AIR FLOW THROUGH THE TUBE, A FLUID MOTOR OPERATES A BUTERFLY VALVE TO RESTRICT THE FLOW OF REFRIGERANT OUT OF THE EVAPORATOR TO RAISE ITS TEMPERATURE TO EVAPORATE THE FROST ON THE EVAPORATOR AND WITHIN THE TUBE.

Nov. 30, 1971 J. H. HEIDORN 3,623,334

HIFIFROST CONTROL RESPONSIVE TO AIR PRESSURE DIFFERENTIAL Filed Nov. 28, 1969 ENGINE 221? I N VEN'TOR.

Z @hnHenzyHe United States Patent Oihce 3,623,334 DEFROST CONTROL RESPONSIVE TO AIR PRESSURE DIFFERENTIAL John H. Heidorn, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich. Filed Nov. 28, 1969, Ser. No. 880,862 Int. Cl. F25d 21/02 U.S. Cl. 62--140 1 Claim ABSTRACT OF THE DISCLOSURE In the preferred form, a tube through which air circulates extends into heat transfer relation with the portion of the evaporator and the suction line. The accumulation of frost within the tube is proportional to the amount of frost which accumulates on the evaporator. A thermostat bulb is mounted in heat transfer relation with the outlet portion of the tube and is normally cooled by the air flow through the tube. It operates a double throw snap switch from the normal refrigerating position to defrost position when the tube reaches a predetermined higher temperature to initiate a defrosting operation. A second control responsive to the difference in pressure in the inlet and outlet portions of the air tube operates a double throw switch which may be connected in parallel with the previously mentioned switch to provide a second defrost air control which operates when the pressure differential increases to a predetermined amount to operate the double throw switch from normal refrigeration position to the defrost position.

In a second form of the invention air is drawn through a tube located in heat transfer with the evaporator by the vacuum of the intake manifold of a gasoline engine. When frost restricts the air flow through the tube, a fluid motor operates a butterfly valve to restrict the flow of refrigerant out of the evaporator to raise its temperature to evaporate the frost on the evaporator and within the tube.

This invention pertains to defrost controls for refrigerating apparatus.

It is an object of this invention to provide a defrost control which is responsive to the actual frost coating of the evaporator to initiate a defrost cycle or to raise the temperature of the evaporator sufficiently to remove any frost therefrom and to prevent the further accumulation of frost.

It is another object of this invention to provide a frost collecting arrangement in which the collection of frost is proportional to the accumulation of frost upon the evaporator for raising the temperature of the evaporator sufficiently to remove the frost therefrom.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIG. 1 is a diagrammatic representation of a refrigerating system together with alternate defrosting controls for defrosting the evaporator; and

FIG. 2 is a diagrammatic view of an automobile air conditioning system with a control embodying another form of my invention for removing frost or preventing the accumulotion of frost upon the evaporator.

Referring now to the drawings and more particularly to FIG. 1, there is shown diagrammatically a sealed unit 20 containing an electric motor which is connected to and drives a compressor. This compressor discharges compressed refrigerant into the condenser 22 from which the Patented Nov. 30, 1971 compressed and liquefied refrigerant flows through a capillary tube restrictor 24 to a finned evaporator 26 where the refrigerant evaporates at a reduced pressure to maintain a temperature sufficiently low to accumulate frost on its surfaces. The evaporated refrigerant is returned to the sealed unit through the suction conduit 28. A centrifugal fan 30 driven by an electric motor (not shown) is provided for drawing air through an inlet 32 and discharging the air through a shroud 34 through the finned evaporator 26.

According to my invention I provide a tube 36, preferably of metal such as aluminum, which extends from the outlet shroud 34 of the centrifugal fan or blower 30 into heat transfer with the coils and a fin of the evaporator 26 and thence to the inlet 32 of the fan or blower 30, with the point of heat exchange being designated by the reference character 38. The outlet portion of the tube 38 has located in heat transfer with it a thermostat bulb 42 extending to a sealed diaphragm 44 which operates a switch lever 46 provided with a snap acting control 48 and a return spring 50 provided with a spring adjustment knob 52.

Frost will accumulate on the below freezing surfaces of the evaporator 26 and inside the tube 36 at substantially the same rate. The air flowing through the tube 36 will normally keep the thermostat bulb 42 cool. Under such circumstances current normally flows from the supply conductor 54 through the normally closed switch 56 to the switch member 46 which is normally in contact with the refrigeration contact 58 connected through the conductors 60 and 62 with the sealed motor compressor unit 20. The sealed motor compressor unit 20 has a second conductor 64 connecting with the second supply terminal 66. The conductor 64 is provided with a suitable thermostatic control 68 for normal control of the system.

When frost accumulates on the evaporator 26 and in the tube 36 adjacent points of contact with the evaporator 26 and the suction line 28, the accumulation of frost within the tube restricts the area within the tube and thereby restricts the flow of air within the tube 36. This causes a rise in temperature of the thermostat bulb 42 as the frost accumulates. When a sufficient amount of frost accumulates, the air flow within the tube 36 will greatly reduce, thereby increasing the temperature of the bulb 42 until the diaphragm 44 attains sufficient pressure and expansion to operate the double throw switch lever 46 away from the contact 58 into contact with the defrost contact 70 which connects through the conductors 72 and 74 with an electric defrost heater 76 located beneath the evaporator 26 in the outlet shroud 34 of the blower 30, which causes the evaporator 26 to be heated sufficiently to defrost.

When the defrosting is completed the temperature will rise thereby opening a defrost limiter thermostatic switch 78 which normally connects the defrost heater 76 with the supply conductor 66 through the conductor 80. When the evaporator 26 is heated the tube 36 will likewise be heated thereby removing the frost from within the tube and also removing the restriction to air flow within the tube 36. The restoration of air flow through the tube 36 again cools the thermostat bulb 42 causing the sealed diaphragm 44 to contract thereby moving the switch lever 46 away from the defrost contact 70 and into contact with the refrigerating contact 58.

The conductor 54 also connects to a second switch 82 which may be closed to connect to the switch lever 84 which is normally biased in contact with the refrigerating contact 86 by a spring 88 which is adjusted by a threaded adjusting screw and knob 90. The switch 56 may be opened to disconnect the switch lever 46 if desired. The switch lever 84 is also provided with a snap acting spring 92. The switch lever 84 is operated by opposed diaphragms. The upper diaphragm 94 is connected by the tube 96 with the inlet portion 98 of the tube 36 on one side of the heat transfer contact with the evaporator 26. The lower diaphragm 111 is connected by a tube 113 to the outlet portion 40 of the tube 46 which connects with the inlet 32 of the centrifugal fan or blower 34.

As long as the tube 36 is substantially free of frost there will be only a very small difference in pressure in the inlet and outlet portions of the tube 36. However, as the frost accumulates, the pressure within the inlet portion 98 will rise and the pressure in the outlet portion 40 will fall. This will cause a corresponding rise in pressures in the tube 96 and the sealed diaphragm 94 and a corresponding fall in pressure in the tube 113 and the sealed diaphragm 111. This will cause a differential in force between the two diaphragms 94 and 111 with the downward force increasing until the switch lever 84 is moved downwardly away from its normal contact with the refrigerating contact 86. The arrangement of the snap action spring 92 causes the switch lever 84 to snap downwardly into engagement with the defrost contact 115 which connects through the conductor 117 to the conductor 74 to energize the defrost heater 76 and to heat the evaporator 26 sufficiently to remove the frost from the evaporator 26 and the tube 36'. When this frost is removed, the differential is pressure between the diaphragm 94 and 111 will be greatly reduced thereby allowing the spring 88 to return the switch lever 84 from the defrost contact 115 into engagement with the refrigeration contact 36. This restores the normal operation of the refrigerating system.

In the second form of the invention shown in FIG. 2, an automobile gasoline engine 210 is provided with a drive pulley 212 at the front which, through a belt 214 drives the belt pulley of a refrigerant compressor 216. This compressor 216 withdraws evaporated refrigerant from the suction conduit 218 and pumps the compressed refrigerant through a discharge conduit 220 to a condenser 222 of the air cooled type which is normally located in front of the conventional automobile radiator. The bottom of the condenser 222 is connected to a supply conduit 224 with a refrigerant flow control device 226 such as an expansion valve or a capillary tube restrictor which controls the flow of refrigerant into the finned evaporator 228. A fan 230 driven by an electric motor 232 is provided for circulating the air between the fins and the tubes of the evaporator 228.

According to the second form of the invention, a tube 234 is located in heat transfer relation with the ends of the tube and one of the tins of the evaporator 228. This tube 234 is connected by the tube sections 236 and 238 with the intake manifold 24% providing a connection between the carburetor 242 and the inlet valves of the engine 210. The flow of air over the evaporator 228 causes frost to collect thereon at approximately the same rate as the frost accumulates within the tube 234 in response to the maintenance of a below freezing evaporator temperature therein and the flow of air to the intake manifold. When this frost accumulates to an objectionable amount, the frost within the tube 234 will provide a suificient restriction to air flow through the tube 34 so as to cause a proportionate lowering of the pressure Within the tube sections 236 and 238. This will cause the sealed bellows or diaphragm chamber 244 to contract. This diaphragm chamber or bellows is operatively connected by the link 246 to the arm 248 which operates a butterfly valve 250 in the enlarged portion 252 of the suction conduit 218. The butterfly valve 250 is therefore turned counterclockwise an amount sufficient to restrict the flow of refrigerant out of the evaporator 228 sufiicient to raise the temperature of the evaporator 228 above the point at which frosting occurs. Through this arrangement the evaporator 228 is substantially clear of the frost and is maintained sufficiently frost free so that its efiiciency is maintained substantially at all times. The evaporator 228 operates at substantially maximum efficiency since it is automatically maintained by this system and at as low a temperature as can be maintained without accumulating a substantial amount of frost upon its surfaces.

While the embodiments of the invention as herein disclosed constitute preferred forms, it is to be understood that other forms might be adopted.

I claim:

1. A refrigerating system including a compressor, a condenser, a refrigerant flow control device and an evaporator connected in an operative refrigerant circuit, a shroud for directing a flow of air through said evaporator, a fan having an inlet for drawing air from a relatively humid compartment to be cooled and an outlet for discharging air into said shroud whenever said refrigerating system is operative whereby frost inherently accumulates upon said evaporator, a tube with its outlet connected to the fan inlet and its inlet connected to the fan outlet which causes air to flow through said tube whenever said fan is operative, a portion of said tube contacting said evaporator in good heat transfer relation to said refrigerant circuit to cause frost accumulation therein as the humid air passes by said portion of said tube, means located downstream from said portion and responsive to a predetermined restriction of air flow through said tube caused by the frost accumulation therein for increasing the temperature of said evaporator periodically for defrosting.

References Cited UNITED STATES PATENTS 2,744,389 5/1956 Raney 62140 3,250,083 5/1966 Orth 62-140 X 3,377,817 4/1968 Petranek 62-440 MEYER PERLIN, Primary Examiner US. Cl. X.R. 62156, 276 

